About winderjssc

Jessica Winder has a background in ecological studies in both the museum and the research laboratory. She is passionate about the natural world right on our doorsteps. She is enthusiastic about capturing what she sees through photography and wants to open the eyes of everyone to the beauty and fascination of nature. She is author of 'Jessica's Nature Blog' at http://natureinfocus.wordpress.com. Jessica has also extensively researched macroscopic variations in oyster and other edible marine mollusc shells from archaeological excavations as a means of understanding past exploitation of marine shellfish resources. She is an archaeo-malacological consultant through Oysters etc. and is publishing summaries of her shell research work on the WordPress Blog called 'Oysters etc.' at http://oystersetcetera.wordpress.com 'Photographic Salmagundi' at http://photosalmagundi.wordpress.com is a showcase of photographs and digital art on all sorts of subjects - not just natural history.

Garretstown Strand Rocks – Part 1

Natural patterns in rocks

These striped grey and yellow patterns in the bedrock at Garretstown Strand in County Cork are made by alternating layers of sand and mud, sometimes in rippled layers. They belong to the Cork Group of rock strata, most probably the White Strand Formation which is comprised mainly of Namurian (Upper Carboniferous) sandstones inter-bedded with brittle, commonly pyritic grey-black mudstones.

REFERENCE

Sleeman, A. G. and Pracht, M. et al (1994)  Geology of South Cork: a description of South Cork and adjoining parts of Waterford to accompany the bedrock geology 1:100,000 scale map series, Sheet 25, South Cork, Geological Survey of Ireland, White Strand Formation pp 23-24.

Natural patterns in rocks

Natural patterns in rocks

Natural patterns in rocks

Natural patterns in rocks

Natural patterns in rocks

Natural patterns in rocks

COPYRIGHT JESSICA WINDER 2014

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Sea Creatures in St Fin Barre’s Cathedral

Mosaic of a lobster

In front of the altar of St Fin Barre’s Cathedral in Cork City, Ireland, is a wonderful mosaic floor made by craftsmen from Udine in the north-east of Italy, using marble from the Pyrenees. The mosaic represents a vision of heaven as described by St Matthew, likening it to a net that has been cast into the sea gathering every kind of creature. Here are a few photographs of the sea creatures depicted.

Mosaic fish

Mosaic fish

Mosaic seashell

Mosaic fish

The mosaic floor before the altar in St Fin Barre's Cathedral

COPYRIGHT JESSICA WINDER 2014

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Rhyolite rock colour, pattern & texture

Rhyolite volcanic rock with red streaks

East of Kilmurrin Cove in County Waterford, Ireland, lies the village of Bunmahon with its roadside Geological Garden and the Copper Coast Geopark Centre. The Bunmahon Geological Garden is like an open-air museum with examples of the main rock types to be found in the area with explanatory sign boards along the way. It is great to be able to compare what has been seen on the local beaches with this named reference collection; it means that  visitors can begin to put together a picture that explains the surrounding landscape through which they are travelling.

The close-up details so easily seen in these labelled rocks also helps with the identification of the rock types represented by the pebbles on the beaches. The rhyolite boulders in particular attracted my attention, providing clues to the wide range of textures and colours to be found in this local Ordovician volcanic rock. I loved the yellow to red streaks and abstract patterns in some of the boulders and the way that the surface of the massive stones has been decorated by small patches of dark grey lichen.

Rhyolite boulder in the Bunmahon Geological Garden

Close-up of rhyolite rock texture

Close-up of rhyolite rock texture

Rhyolite boulder in the Bunmahon Geological Garden

Close-up of rhyolite rock texture

Rhyolite boulder in the Bunmahon Geological Garden

Close-up of rhyolite rock

Close-up of rhyolite rock

Close-up of the texture of rhyolite rock

Boulders of rhyolite rock in Bunmahon Geological Garden

Natural pattern in a rhyolite boulder in the Bunmahon Geological Garden

Natural abstract pattern in a rhyolite boulder in Bunmahon Geological Garden

Abstract pattern in rhyolite rock

COPYRIGHT JESSICA WINDER 2014

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Pebbles at Kilmurrin Cove – Part 2

Wet beach stones of volcanic rock

Here are some more examples of the pebbles at Kilmurrin Cove on the Copper Coast in County Waterford, Southern Ireland (see the previous post). Again, most of them seem to be volcanic rocks of Ordovician age, derived from the underlying bedrock of the beach and the outcrops in the surrounding cliffs, and including rhyolite in its solidified lava form and also as consolidated volcanic ash and breccias. Some stones may be of different geological types and origins, having been brought from much further afield and deposited by melting ice sheets.

This time most of the beach stones were photographed at the western end of the beach where  the stream or small river, that is dammed-up behind the pebble bank, surfaces through the stones and makes a break for the sea via jagged outcropping bedrock. The water is stained tea-colour by the peat through which it has flowed down the glaciated valley.

Click on the pictures to enlarge them and see the description.

Pebbles underwater in a beach stream

Dry beach stones with frond of seaweed

Wet beach stones and pebbles on the beach

Wet beach stones in a cove rimmed by cliffs of Ordovician rock topped by glacial deposits

Kilmurrin Cove pebbles on the Copper Coast in Ireland

Dry beach stones with washed up kelp

Pebbles with spots and stripes at Kimurrin Cove

Wet beach stones of mainly Ordovician volcanic origin

Pebbles underwater in a beach stream

Wet beach stones at Kilmurrin Cove

Wet beach stones at Kilmurrin Cove

Wet pebbles with sea foam bubbles at Kilmurrin Cove

COPYRIGHT JESSICA WINDER 2014

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Pebbles at Kilmurrin Cove – Part 1

Spotty rhyolite pebble with phenocrysts

Continuing with my Irish pebble and rock theme, trying to understand the phenomena I encountered on my travels, I noticed lots of patterned pebbles on the next shore along the Copper Coast at Kilmurrin Cove in County Waterford. Many of the beach stones had natural patterns based on either spots or stripes, or a combination of the two. As far as I can make out, the spot pattern is due to a phenomenon where thick viscous lava from a volcano is extruded and cools quickly trapping many gas bubbles. The shape of the bubbles is preserved in the solidified lava. Over time, the gas is replaced by minerals such as clear quartz, salmon-coloured K-feldspar, off-white sodium-rich plagioclase, or natural glass, which crystallise in the spaces initially created by the gases. Sometimes the bubble shapes have merged in the lava giving odd shaped spaces for the new minerals to fill.

Rhyolite is one of the rocks in which this happens.  It has the same chemical composition as granite but because it is an extrusive rock and cooled quickly, the crystals of the matrix of the rock cannot be distinguished. [Whereas granite is an intrusive rock that cooled slowly giving rise to a rock composed entirely of large visible crystals]. The crystals that make up the solidified lava form of rhyolite are so small that they cannot be seen with the naked eye or even with a hand lens. However, the minerals that have percolated into the bubble spaces are macroscopic, they can easily be seen. I think the types of crystals like those shown in image 1.1 are called spherulites; these  spherulites are rounded bodies, often coalescing, comprising radial aggregates of needles, usually of quartz or feldspar. Spherulites are generally less than 0.5 cm in diameter, but they may reach a metre or more across – though not in this part of the world as far as I know. These relatively regular structures in the rock can be compared with isolated large crystal inclusions that are known as phenocrysts.  Rhyolite with phenocrysts is called porphyritic rhyolite.

A number of the pebbles have parallel lines or swirling layers defined by varying colour or granularity – maybe with spherulites as well. These rhyolite pebbles may be showing flow banding that appears like linear or striped patterns when seen in cross-sections of the rock. The lines have been described as being similar to tree rings. This type of rock is called banded rhyolite and forms from slow flowing lava in which bubble- and crystal-rich layers form on the cooling surface. Multiple flows build up one on top of the other to create the multiple lines. At least that is what I think is shown in these striped pebbles. I am open, as always, to correction. I suppose I can’t rule out that some of the lines I noticed might be Liesegang rings.

Not all rhyolite rocks are solid forms of lava. Rhyolites are mostly tuffs and breccias rather than lavas. Rhyolitic Tuffs are rocks consisting of consolidated volcanic ash ejected from vents during a volcanic explosion, while rhyolitic breccias are composed of larger angular fragments thrown out by the explosions. I’ll talk more about this subject later when I write about my visit to Bunmahon Geological Garden further along the Copper Coast.

As usual, click on the pictures to enlarge them and see the description for the image.

Natural patterns, shapes and textures in pebbles on the beach

Beach stone with stripes and spots

View of a pebble beach on a Copper Coast in Southern Ireland

Pebble bank on the shore at Kilmurrin Cove

Dry beach stones on the Copper Coast in Ireland

Natural patterns, shapes and textures in pebbles on the beach

Natural patterns, shapes and textures in pebbles on the beach

Natural pattern of banding in a rhyolite pebble

View of the west end of Kilmurrin Cove showing river dammed by large pebble bank.

View of the west end of Kilmurrin Cove with stream crossing exposed Ordovician rocks

Natural patterns, shapes and textures in pebbles on the beach

Dry beach stones on the Copper Coast in Ireland

COPYRIGHT JESSICA WINDER 2014

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A Copper Coast Geopark Sculpture

 

We swerved off and parked a while to get a closer look at this fantastic sculpture as we drove along the coast road between Annestown and Bunmahon in southern Ireland. The monumental block of limestone with brightly coloured mosaic inlays is called “Ice, Fire and Water” has been carved by Colette O’Brien. It stands overlooking Dunabrattin Head near Boatstrand, and symbolises the elemental forces that gave rise to this spectacular stretch of rocky shoreline, and celebrates the establishment of the Copper Coast Geopark of which it is a part.

COPYRIGHT JESSICA WINDER 2014

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Rock Textures at Annestown

Close-up of Ordovician volcanic rock texture in cliffs at Annestown

The cliffs at Annestown Beach in County Waterford, which are part of the 25 kilometre stretch of the Copper Coast Geopark, are Ordovician in age. This is a very early period of land formation dating from between 460 to 450 million years ago when a volcano on the seabed near to the South Pole erupted with a violent explosion that forced a mixture of ashes, rock fragments and debris through the water to the surface of the ocean and this material fell back on the water to settle on the seabed. Molten lava in the form of rhyolite was also extruded to join this layer of volcanic debris. Through almost unimaginable periods of time, this layer consolidated to form rock, was moved along with the tectonic plate on which it rested to its present position in the northern hemisphere, and was raised to the surface. Quite a journey and a fantastic story, don’t you think?

Close-up of Ordovician volcanic rock texture in cliffs at Annestown

Close-up of Ordovician volcanic rock texture in cliffs at Annestown

Close-up of Ordovician volcanic rock texture in cliffs at Annestown

Close-up of Ordovician volcanic rock texture in cliffs at Annestown

COPYRIGHT JESSICA WINDER 2014

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The Sea Wall at Annestown

Pebble bank on the seashore retained by a seawall

The pebble bank on the seashore at Annestown is retained by a low sea wall that curves from one end of the bay to the other. (You can see it on the right of the picture above). It stops incursions by the sea in rough weather, and also prevents the movement of the pebbles inland. The car park is mostly tucked behind the sea wall but where an opening allows access to the beach, recent winter storms and wave-borne beach stones have pounded and ripped-up the tarmac.

A footpath follows the landward side of the wall from east to west. The wall is high enough to fulfill its function and low enough to allow walkers to enjoy the view at all times. The construction of this sea defence is interesting, seemingly made up from individual blocks of small pebbles in a cement matrix, and the blocks then cemented together to form the wall. It looks as though the wall is using local materials in an attempt to blend better with the surroundings. However, the rough surface is colonised extensively by black, yellow, and white lichens whose distribution varies, presumably according to the degree of exposure to prevailing sun and wind and rain, making the wall stand out as a feature rather than merge with the landscape – although there is a certain resonance with the dark cliffs and headlands beyond.

The pebbles on the seashore at Annestown, banked up against a sea wall

View of the sea wall at Annestown looking west

View of the sea wall at Annestown looking east

Close-up of lichens on a sea wall

Close-up of lichens on a sea wall

Close-up of lichens on a sea wall

COPYRIGHT JESSICA WINDER 2014

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Pebbles at Annestown

Pebbles on a Copper Coast beach

The first beach that I visited on my recent trip to Ireland was near the small village of Annestown in County Waterford. It is part of the Copper Coast Geopark, and I wish I had known at the time that the Geopark website offers informative trail guides and an audio podcast to guide visitors on a walk around this particular area, starting at that very beach.

I was immediately struck by how different the rocks in the cliff are from anything I have seen before, and the pebbles on the windy and surf-washed shore have their own unique character. A sign-board in the car-park explains that the rocks in this location are extremely old, mostly dating from the Ordovician Period, resulting from ocean-bed volcanic eruptions at a time when the land which is now Ireland was formed near the South Pole between 460 and 450 million years ago. Movements of the earth’s crustal plates over vast eons of time have caused the land to gradually migrate northwards to its current position.

In amongst the pebbles of volcanic origin and Ordovician age are others from sources further along the coast and also, no doubt, pebbles derived from the deposits of clay, boulders, and sand that were dumped over the land surface at the end of the Ice Age 12,000 years ago as the ice melted, and which can be seen today as a yellow-brownish layer on top of the cliffs.

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

COPYRIGHT JESSICA WINDER 2014

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At Dogs Bay

Dogs Bay in Connemara has a wonderful white sandy beach composed of the tiny shells of microscopic one-celled creatures that live mostly on the mud of the ocean bed. These animals are called Foraminifera. When they die, millions upon millions of their calcium skeletons, bearing many chambers and holes, and not visible to the naked eye, wash ashore to form this unusual sand. This is such a rare occurrence that Dogs Bay beach is the only one composed of foraminifera in the northern hemisphere.

The bedrock of the land around this wonderful white sandy shore is made up of volcanic rocks including granite that has many different colour forms and patterns due to the different mineral crystals that it contains – if you get up really close to see it. The granite outcrops on the shores often have a rounded surface where ice sheets or glaciers passing over them have ground them smooth. The waterside rocks form attachments for a variety of seaweeds, along with many seashore creatures, particularly gastropod molluscs like periwinkles and limpets, whose brightly-coloured empty shells accumulate at the base of boulders low down in the intertidal zone.

COPYRIGHT JESSICA WINDER 2014

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